Building Ray from Source

For a majority of Ray users, installing Ray via the latest wheels or pip package is usually enough. However, you may want to build the latest master branch.


If you are only editing Python files, follow instructions for Building Ray (Python Only) to avoid long build times.

Building Ray (Python Only)


Unless otherwise stated, directory and file paths are relative to the project root directory.

RLlib, Tune, Autoscaler, and most Python files do not require you to build and compile Ray. Follow these instructions to develop Ray’s Python files locally without building Ray.

  1. Pip install the latest Ray wheels. See Daily Releases (Nightlies) for instructions.

pip install -U
  1. Fork and clone the project to your machine. Connect your repository to the upstream (main project) ray repository.

git clone[your username]/ray.git
cd ray
git remote add upstream
# Make sure you are up-to-date on master.

3. Replace Python files in the installed package with your local editable copy. We provide a simple script to help you do this: python python/ray/ Running the script will remove the ray/tune, ray/rllib, ray/autoscaler dir (among other directories) bundled with the ray pip package, and replace them with links to your local code. This way, changing files in your git clone will directly affect the behavior of your installed ray.


Do not run pip uninstall ray or pip install -U (for Ray or Ray wheels) if setting up your environment this way. To uninstall or upgrade, you must first rm -rf the pip-installation site (usually a site-packages/ray location), then do a pip reinstall (see 1. above), and finally run the above script again.

cd ray
python python/ray/
# This replaces miniconda3/lib/python3.7/site-packages/ray/tune
# with your local `ray/python/ray/tune`.

Building Ray (full)


If you are only editing Tune/RLlib/Autoscaler files, follow instructions for Building Ray (Python Only) to avoid long build times.

To build Ray, first install the following dependencies.

For Ubuntu, run the following commands:

sudo apt-get update
sudo apt-get install -y build-essential curl unzip psmisc

pip install cython==0.29.0 pytest

For MacOS, run the following commands:

brew update
brew install wget

pip install cython==0.29.0 pytest

For Windows, see the Windows Dependencies section.

Ray can be built from the repository as follows.

git clone

# Install Bazel.
# (Windows users: please manually place Bazel in your PATH, and point BAZEL_SH to MSYS2's Bash.)

# Build the dashboard
# (requires Node.js, see for more information).
pushd ray/dashboard/client
npm install
npm run build

# Install Ray.
cd ray/python
pip install -e . --verbose  # Add --user if you see a permission denied error.

The -e means “editable”, so changes you make to files in the Ray directory will take effect without reinstalling the package.


if you run python install, files will be copied from the Ray directory to a directory of Python packages (/lib/python3.6/site-packages/ray). This means that changes you make to files in the Ray directory will not have any effect.

Fast, Debug, and Optimized Builds

Currently, Ray is built with optimizations, which can take a long time and interfere with debugging. To perform fast, debug, or optimized builds, you can run the following (via -c fastbuild/dbg/opt, respectively):

bazel build -c fastbuild //:ray_pkg

This will rebuild Ray with the appropriate options (which may take a while). If you need to build all targets, you can use "//:*" instead of //:ray_pkg.

To make this change permanent, you can add an option such as the following line to your user-level ~/.bazelrc file (not to be confused with the workspace-level .bazelrc file):

build --compilation_mode=fastbuild

If you do so, remember to revert this change, unless you want it to affect all of your development in the future.

Using dbg instead of fastbuild generates more debug information, which can make it easier to debug with a debugger like gdb.

Building the Docs

If you make changes that require documentation changes, don’t forget to update the documentation!

When you make documentation changes, build them locally to verify they render correctly. Sphinx is used to generate the documentation.

cd doc
pip install -r requirements-doc.txt
pip install -U -r requirements-rtd.txt # important for reproducing the deployment environment
make html

Once done, the docs will be in doc/_build/html. For example, on Mac OSX, you can open the docs (assuming you are still in the doc directory) using open _build/html/index.html.

Using a local repository for dependencies

If you’d like to build Ray with custom dependencies (for example, with a different version of Cython), you can modify your .bzl file as follows:

  name = "cython",
) if False else native.new_local_repository(
  name = "cython",
  build_file = "bazel/BUILD.cython",
  path = "../cython",

This replaces the existing http_archive rule with one that references a sibling of your Ray directory (named cython) using the build file provided in the Ray repository (bazel/BUILD.cython). If the dependency already has a Bazel build file in it, you can use native.local_repository instead, and omit build_file.

To test switching back to the original rule, change False to True.